I have a problem with my beautiful pearscale , i recently introdued some fantailed orandas to my tank and they have constantly chased and harassed my pearlscale to the point where exhaustion and stress is becoming very apparent .

is there a reason for all this as i did alot of research and i was confident these fish would be compatible

120L tank will help for a while, but will not be big enough in the longer term; you will need a filter turning over 10x the tank volume viz 1200L/h

you should aim for a 250 to 300 L tank if you wish to keep these fish

In the meantime you should be checking your water parameters and looking to change 25-50% of the tank-water every couple of days..your fish are most likely experiencing toxic shock owing to the high bio-load

Pearl scales are much rounder than orandas, and may for that reason be slower and thought of as weaker by their tank mates.I would also suggest an upgrade so that they'll have some more space and don't have to feel stressed about sharing that small tank.I'd go for nothing smaller than a 200-250 liter tank for these fish, orandas grow very big and pearl scales will reach sizes similar to large oranges when adult.